Latex paints employ latex binders as film formers, pigment binders, fillers and the like. Latex binders are typically comprised of emulsion polymers. The properties that are desirable in latex binders used in paints are, uniform particle size, excellent mechanical stability (especially at high shear) and no coagulum. Additionally, the latex should dry to a clear, glossy and water resistant film. The properties that are desirable in latex-based coating compositions are freeze-thaw stability, good gloss, superior abrasion resistance, good block resistance, controlled drying time and good rheology.
Conventional anionic sufactants have been used to control the latex particle size and to stabilize the latexes at high solid contents. However, such anionic surfactants are not covalently bound to the polymer particles. Under high shear or under a few cycles of freeze-thaw tests, the anionic surfactants can be desorbed and their stabilizing properties in a latex system are lost. Moreover, such conventional surfactants are required to be present in an amount of at least about 3 pphm in the polymerization of the latex which has an adverse effect on the water resistance of the coating prepared using the latex due to the hydrophilicity imparted by the surfactant, and the unbound surfactant has a tendency to migrate to the surface of the coating in order to lower the surface tension.
An article in Advanced Materials, entitled "Microemulsion Polymerization: New Surfactant Systems by Counterion Variation", Vol. 8, No. 10, pp. 840-844 (1996), describes adjusting the geometry and polarity of a given surfactant by electrostatic coupling with the appropriate organic counter-ion, such as the generation of a very bulky, hydrophobic head group. Selected modifications of two standard surfactants, dodecyl sulfate and cetyl trimethylammonium ions were described. The process was micromulsion polymerization process.
An article in Progress in Organic Coatings entitled, "Polymerizable Surfactants", Vol. 20, pp. 325-337 (1992), describes the design of polymerizable surfactants and demonstrate their applicability in selected applications, such as alkyd emulsions, micro-emulsions of alkyds, emulsion polymerization and surface modification. Surface modification includes the polymerization of a monolayer adsorbed from aqueous solution and the crosslinking surfactants that have migrated to the surface.
An article in Macromolecular Chemistry, Macromolecular Symposium entitled, "Polymeric Surfactants in Emulsion Polymerization", Vol. 35/36, pp. 467-475 (1990), describes the stabilizing efficiency of a variety of amphipathic copolymers in aqueous emulsion polymerizations of styrene, methyl methacrylate and acrylonitrile. Using the number and the size of the particles as the criterion of stability, it was determined that the availability for anchoring of the backbone in the amphipathic graft copolymers was crucial for stability. A change in the backbone chain length with the same percent hydrophilic grafts was determined to have no effect on the outcome of the reaction.
An article in the Australia Journal of Chemistry entitled, "A Novel Composite Polymer Latex Technology", Vol. 42, pp. 2055-70 (1989) describes a polymerization process for preparing a latex wherein each particle contains a blend of two or more copolymers. The particles are sterically stabilized by a non-ionic reactive surfactant. The latex is prepared by suspension polymerization.